My general knowledge has been that once the diameter gets to 1/4", then=20 they're called bolts, and then they're usually hex head. Yes there are=20 exceptions. Taught to me by a machinist some years ago. However, I also=20 call a 10-32 screw a screw, because the local hardware store (Home=20 Depot) calls them that. For full context on this situation, the purchase list included "10-32 x=20 1" pan-head screws ". The teacher said that she had no idea what I=20 wanted, so bought #10 screws (sheet metal), and 10-32 "bolts", and said=20 that I was not specific. Saying no prob, that I just needed the 10-32=20 (screws) that she got, she argued that I should've said "bolts", and=20 those are not screws. Even after showing her that the package actually=20 said "machine screws", she demanded that they're bolts. I could not=20 bother to get into it beyond that. I suspect we're no longer on PIC topic tag anymore though. On 3/7/2016 12:16 PM, Sean Breheny wrote: > https://en.wikipedia.org/wiki/Screw#Differentiation_between_bolt_and_scre= w > > In the US anyway, the core distinction is traditionally whether the > fastener _needs_ a nut and is held still during tightening (bolt) or is > intended to screw into threads in the materials being joined (either with > pre-cut threads or by thread-forming) (screw). Some things are clearly > bolts (carriage bolts since they cannot be screwed into a threaded hole d= ue > to their lack of a driving feature and their square feature on the shaft > near the head). Some things are clearly screws (like wood screws or > self-tapping sheet metal screws). Other things are not so clear (like > typical pan-head machine screws which may also use nuts) > > > On Mon, Mar 7, 2016 at 10:56 AM, wrote: > >>> Maybe this is regional. I grew up in a junk yard. We had machine screws= , >> not >>> to be confused with wood screws, and bolts. Bolts were big. Machine >> screws >>> were small. >> My understanding of the difference is that screws need a screwdriver, fl= at >> blade or cross blade (Pozi-drive etc.). >> >> Bolts require a spanner as they have a hex head, or require an Allen key >> or similar tool, as they have a socket head, or don't have a means of >> driving, but require a nut on the other end, e.g. coach bolts. >> >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .